Gene transfer has offered great promise in the genetic manipulation of organisms. The movement of genes within plant species has played an important role in crop improvement for many decades. The recombinant DNA methods which have been developed have greatly extended the sources from which genetic information can be obtained for crop improvement. Gene transfer systems based on recombinant DNA are available for several crop species and are under development for many others.
Rapid progress has been made in developing the tools for manipulating genetic information in plants. Plant genes are being cloned, genetic regulatory signals deciphered, and genes transferred from entirely unrelated organisms to confer new agriculturally useful traits to crop plants. Recombinant DNA methods significantly increase the gene pool available for crop improvement.
A variety of methods have been developed for the transformation of plants and plant cells with DNA. Generally, the most success has been in dicotyledonous plants. Some success has been reported with certain monocotyledonous cereals.
Cereals comprise a commercially valuable group of plant species that could benefit from the introduction and expression of foreign genes controlling improved grain quality and such agronomically important traits as tolerance to disease, insects, herbicides, and stress. However, most cereals have not proven readily amenable to either Agrobacterium-mediated gene delivery, or to the routine regeneration of fertile transgenic plants from directly transformed protoplasts. The use of microprojectile-bombardment-mediated transformation of embryogenic tissue culture material, with the subsequent regeneration of transgenic plants, has overcome the regeneration problems associated with the production of plants from cereal protoplasts. Using this technology, transgenic plants have been obtained from microprojectile-bombarded tissue cultures of many species.
Many of the recent advances in plant science have resulted from application of the analytical power of recombinant DNA technology coupled with plant transformation. These approaches facilitate studies of the effects of specific gene alterations and additions on plant development and physiology. They also make possible the direct manipulation of genes to bio-engineer improved plant varieties.
While strides have been made in the genetic transformation of plants, it is by no means a routine matter. In fact, transformation efficiency is quite low making the process very labor intensive. Some reports indicate that the current transformation methods provide only a transformation frequency of about one event from every thousand bombarded embryos. This transformation frequency is too low for many genetic studies and for routine commerical applications. Therefore, a method is needed to improve the efficiency of genetic transformation.